1. Field of the Invention
The present invention relates to an image forming apparatus of an electrophotographic type employed in a copying machine and method, etc., and in particular to an image forming apparatus including a transferring section thereof.
2. Description of the Background Art
An image forming apparatus of an electrophotographic type is known in which a toner image is formed on an image carrier, such as a photosensitive drum, and is transferred onto a transfer belt, and in which the toner image transferred onto the transfer belt is further transferred onto a transfer paper, see for instance as described in the published specifications of Japanese Laid-Open Patent Publication Nos. 64-40848/1989 and 6-348148/1994. An image forming section included in background transfer units of such image forming apparatuses is explained referring to FIG. 3.
FIG. 3 is an outline structural diagram illustrating a background image forming section in an image forming apparatus utilizing laser light. In FIG. 3, developing apparatuses 52 and 53 respectively accommodate therein developers of different colors. A laser light generating section 55 reads out image data from an original document by use of a scanner (not shown in FIG. 3) and exposes a photosensitive drum 51 with optical image data through a mirror 54. A cleaner 56 cleans a surface of the photosensitive drum 51, and a transfer belt 57 is disposed such that a part of the transfer belt 57 is brought into contact with the photosensitive drum 51.
An eraser 58 radiates an erasing light onto the photosensitive drum 51 so that toner is not put on a portion not to be formed with an image thereon. The eraser 58 is disposed between the radiating portion of the photosensitive drum 51, onto which the light from the laser light generating section 55 impinges, and the developing apparatus 52. Further, a peeling-off claw 59 peels off transfer paper (not shown) attached to the photosensitive drum 51 and is positioned between the cleaner 56 and the transfer belt 57. Moreover, a charge removing charger 61 and a charging charger 62 are disposed between the cleaner 56 and the developing apparatus 52 in a rotating direction when the photosensitive drum 51 rotates in the clockwise direction as shown by the arrow in FIG. 3. A further charging charger 63 and LED array 64 are disposed between the developing apparatuses 52 and 53 in the rotating direction of the photosensitive drum 51.
The transfer belt 57 is constructed with an elastic substance and is suspended between a driving roller 65 and a driven roller 66 with a suitable tension. A transfer roller 67 for applying a transfer bias voltage and a cleaning blade 68 for scraping off toner from a surface of the transfer belt 57 are arranged around the transfer belt 57. A support frame 69 is disposed on a lower surface of the transfer belt 57 so as to surround the transfer belt 57. The support frame 69 is mounted rotatably on an image forming apparatus main body (not shown) so as to descend on the driven roller 66 side by an action of rotating around the supporting shaft 71 at the side of the driving roller 65 as a fulcrum.
The driven roller 66 side of the transfer belt 57 is elastically pressed against the photosensitive drum 51 by action of a pressing spring 72. The reference numeral 73 represents an attaching/detaching lever for releasing the pressing force of the pressing spring 72 at a time of a waiting state. If the pressing force of the pressing spring 71 is released by handling the attaching/detaching lever 73, the transfer belt 57 is rotated by a force of its weight thereof around the driving roller 65 as a fulcrum, and thereby the transfer belt 57 is separated from the photosensitive drum 51. The reference numeral 74 represents an opening lever for separating the transfer belt 57 from the photosensitive drum 51, and 75 represents a pair of registration rollers for feeding transfer paper from a paper feeding tray (not shown) to the transfer section.
As mentioned heretofore, the background image forming apparatus of the transfer belt type has adopted a mechanical structure in which transfer belt 57 is pushed from a lower position and brought into contact with the photosensitive drum 51 and the transfer paper passes between the transfer belt 57 and photosensitive drum 51. For this reason, in a case that a transfer paper jamming occurs during a time period when an image forming operation is performed, as operations in removing the jammed paper, a front cover (not shown) of the machine main body is opened at first, and then the transfer belt unit is separated from the photosensitive drum 51 by use of the opening lever 74. Then, by an operator looking into the interior of the machine in order to confirm the existence of jammed paper, the jammed paper is removed if it exists in the machine. In this way, it is necessary to perform these three working processes as mentioned above to remove a jammed paper. After removing the jammed paper, the above working processes are performed in the reverse order, for returning the machine to its initial state. These are the working processes of the background machine.
However, according to the aforementioned working processes, it is often difficult for an operator to understand the required method of handling the opening lever 74, and it is also difficult to recognize the position of the jammed paper as the interior of the machine is dark. Furthermore, if it is necessary for the operator to put his/her hand(s) in the interior of the machine in order to remove the jammed paper, the operator's hand is apt to be injured or made dirty on some occasions. Moreover, the operator may often forget to return the opening lever 74 to its closed position after the jammed paper is removed. On this occasion, the front cover has to be opened again in order to return the opening lever 74 to its closed position. In addition, if the rotative fulcrum of the transfer belt 57 for attaching to and detaching from the photosensitive drum 51 is simply set to the machine main body, a phenomenon may occur several times that the transfer paper is electrostatically absorbed onto the transfer belt 57 and is transported thereby after being put between the rollers of a fixing section. In such a situation, if the driving roller 65 of the transfer belt 57 and the rollers of the fixing section are not disposed in parallel with each other, such a state results in an occurrence of folding and/or wrinkling of the transfer paper or an occurrence of shifting of the transfer belt 57.
Furthermore, although the aforementioned transferring apparatus disclosed in the published specification of Japanese Laid-open Patent Publication No. 6-348148/1994 includes a pressurizing section for elastically pressurizing the transfer belt 57 onto the photosensitive drum 51, the force of gravity is utilized to separate the transfer belt 57 from the photosensitive drum 51. For this reason, depending on the direction of bringing the transfer belt 57 into contact with the photosensitive drum 51, even though the pressurizing section for pressurizing the transfer belt 57 is released, no force is exerted on the transfer belt 57 in the direction of being separated from the photosensitive drum 51, and thereby a troublesome matter due to incorrect releasing occurs on some occasions.